This project will contribute to an understanding of the developmental genetics responsible for phenotypic variation. As such, the project will have contributions well beyond the scope of the specific questions addressed given that many diseases are the result of problems in gene expression. Using wing pattern variation in an ideal system, the cabbage white butterfly (Pieris rapae), this project will dissect the genetic control of variation through several approaches. First, experimental endocrinology will be used to investigate the hormonal control of phenotypic variation. Second, immunohistochemistry will be utilized to assay temporal and spatial patterns of expression of candidate wing pattern genes. Third, transgenic lines of the butterflies will be generated so that ultimately, hypotheses of gene function generated from the expression assays can be tested. Because of its relatively simple wing patterns, this species will serve as an ideal comparative model to more established butterfly model systems with more complex patterns, helping to elucidate how more complex traits evolve and develop from simpler traits through the co-option of regulatory and structural genes.